Certain devices that are operated by a reciprocating element, e.g. a button, require the presence of a counting device in order to provide an indication of the extent of use. Known counting devices range from complex electrical devices providing a visual digital display to simple mechanical devices having a sliding scale to display the count or extent of use.
Many types of medicines may be administered by nasal or oral inhalation. In many cases the medicament is formulated with a suitable propellant and other components and charged in an aerosol vial. The aerosol vial is fitted, typically by means of a valve ferrule, with a valve which comprises a metering chamber such that each operation of the valve, typically through depression of a valve stem, dispenses a predetermined measured quantity of medicament. The aerosol vial is inserted into an adapter having a mouthpiece or a port adapted for nasal use and the medicament is dispensed simultaneously with inhalation.
There are two general types of adapter used with such aerosol vials. A breath-actuated adapter comprises a mechanism that allows the patient to prime the device, and then the aerosol is fired automatically in response to the patient inhaling through the mouthpiece or nasal port. A second type of adapter is a press-and-breathe adapter in which the patient fires the device by manually pressing the aerosol vial whilst inhaling through the mouthpiece or nasal port.
The aerosol vial is initially charged with a known quantity of medicament, a metered dose of which is dispensed each time the valve is operated. Counting the number of operations of the valve will give an indication of the total medicament dispensed and hence of the amount of medicament remaining in the vial. The metering is normally accurate, but incorrect actuation of the valve occasionally results in a reduced dose. However, the dose cannot exceed the predetermined metered quantity when the aerosol device is fired. Therefore, counting the number of doses used is a safe basis for computing the number of doses remaining because any error will indicate the presence of fewer doses than are actually present. It is highly desirable that the patient be given an indication that the contents of the vial are depleted before the vial is actually empty, to prevent the patient attempting to use an empty inhaler at a time when the patient is under stress. Accordingly, it is desirable to incorporate some form of counting device on the aerosol vial or adapter that would give an appropriate indication before the vial becomes empty.
A conventional aerosol valve is operated by causing a valve stem to be depressed relative to the valve body. A convenient means of counting the number of discharges from the aerosol vial is to convert the relative reciprocatory movement between the valve stem and the valve body into a one-way movement of some form of counting device or indicator. If the number of doses contained within the vial were relatively small it would be possible to use linear movement of the vial to index a simple indicator band along and so mark the progression from “full” to “empty”. Such a counting means need only comprise a ratchet device and a toothed indicator rack moving in the direction parallel to the relative reciprocal motion between the valve stem and the valve body. However, the number of doses in an aerosol vial is normally at least fifty and often two hundred. Accordingly, in practice, the total linear movement of such a rack would be far too great to be accommodated in a normal inhaler unless each incremental step of the rack was very small. However, tiny incremental steps require firstly that only a small fraction of the total reciprocatory movement of the valve stem is converted into rack movement and secondly that very fine teeth must be moulded on both mating parts. These requirements are not easy to fulfil economically and on a mass production basis.
In addition to the ability to accurately count many doses it is important that the counting device is not susceptible to false counting, or otherwise presenting incorrect information. False counting can occur due to inaccuracies or malfunctioning of the components of the device, movement of the valve stem insufficient to fire a dose, repeated reciprocation of the valve stem before it has returned to its rest position, back rotation of the indicator during the return stroke of the valve stem, or movement of the dose counter assembly due to vibrations when the device is carried in a pocket or handbag etc. Another design criterion for dose counters used with inhalation devices is that the impact on the airflow through the device must be minimal, so that the aerolisation characteristics of the doses are not affected by incorporating the dose counter into the device.
There have been numerous proposals for inhaler counting devices.
U.S. Pat. No. 5,349,945, WO06/062450, US20020170928 and US20050087191 disclose dose counters incorporating a worm and rack mechanism.
US20050126469, WO93/21980, U.S. Pat. No. 5,871,007, U.S. Pat. No. 6,907,876, GB2348928, US20020189611, U.S. Pat. No. 4,668,218 and WO06/054083 disclose devices in which a cylindrical member having a helix or spiral is used to convert rotary motion into another, generally linear, motion.
WO02/91293, U.S. Pat. No. 6,752,153, GB2348928, WO96/39337, WO06/054083, EP0480488, FR2842905 and U.S. Pat. No. 5,871,007 disclose devices comprising one or more flexible members that operate a mechanism when loaded and spring back when unloaded.
Other counting devices that include some form of ratchet mechanism are disclosed in U.S. Pat. No. 6,446,627, GB2191032, WO06/027313, US20040065326, WO05/084736, U.S. Pat. No. 5,871,007, US20050087191 and US20050126469.
Very few of the proposals have been successfully commercialised. The probable reasons for the lack of commercialisation are difficulty in manufacture, poor reliability and excessive cost.
The present invention has been made with the above points in mind.